In continuous casting (strand casting), a mold is used to cast from the liquid metal a strand that is then pulled out of the mold. One factor that is essential for good quality in a strand cast in this fashion is maintaining a constant pouring level, i.e. the rate at which the liquid metal is poured into the mold. It is already known to regulate the pouring level of the liquid metal. The controller, however, is difficult to design, since the parameters of the controlled system, i.e. the pouring apparatus and the mold, are subject in some cases to extreme fluctuations.
The inflow of liquid metal into a mold occurs, for example, via an inflow nozzle that is immersed into the liquid metal in the mold, and that has outlet openings for the discharge of the liquid metal into the mold. These outlet openings in some circumstances become smaller in the course of a pouring operation due to the settling of solidifying material. Inflow resistance increases, i.e. the controlled system is modified. As the solidified material breaks away from the outlet openings, the inflow resistance abruptly decreases, and abrupt changes occur in the controlled system. Because of these fluctuations in the controlled system, a controller cannot be optimized with respect to the controlled system.